This invention relates to transmission units in which the operative ratio is selected by a selection system which includes fluid-pressure-operated actuators under the control of solenoid-operated valves. Such transmission units are used, for example, in agricultural/industrial tractors.
Whilst such transmission units operate effectively they can be prone to break down due to minor electrical problems, etc. which leave the valves and thus the fluid-pressure-operated actuators inoperative thus completely disabling the transmission unit.
It is an object of the present invention to provide an improved form of such a transmission unit in which the problem of transmission disablement is mitigated.